1. Field of the Invention:
The present invention relates to methods and apparatuses for scanning a body and preferred embodiments relate, more particularly, to methods and apparatuses for determining a non-circular-orbit for scanning a patient.
2. Discussion of the Background:
In some existing systems, gamma cameras are used to form tomographic images of a patient during a nuclear medicine study. In, for example, single photon emission computed tomography (SPECT) systems of the transaxial rotational camera type, a scanning gamma camera head can rotate around a region of the patient to be scanned. Typically, this rotation is in a plane generally orthogonal to a cranial-caudal axis of a patient and results in the imaging of a cross-sectional slice of the patient's body.
In general, for certain detectors, such as, e.g., parallel hole collimated detectors, resolution decreases with distance so that keeping the detector close to the patient can improve resolution and image quality. As addressed by the present assignee in U.S. Pat. No. 5,523,571, it can be desirable for a camera head to be close to a patient's body because this results in increased sensitivity and, consequently, a better image (if the length of the study is held constant) or a shorter study (if the image quality is held constant). In some systems, the orbit of the camera head has been made non-circular with respect to a patient to decrease the average distance between the camera head and the patient.
A few illustrative devices for producing a non-circular orbit are disclosed, e.g., in U.S. Pat. No. 4,503,331 (entitled Non-Circular Emission Computed Tomography), showing, e.g., a “radiation imaging system [that] includes a rotatable scintillation detector and a linearly movable detector stand” and U.S. Pat. No. 4,593,189 (entitled Proximity Detector For A Body Scanner), showing, e.g., “an energy beam emitting and receiving device in front of the scanning surface of the body scanner for an energy beam projected in a plane parallel to the scanning surface” and “[a] signal generator . . . connected with the energy beam emitting and receiving device for generating a proximity signal when the energy beam becomes weakened or interrupted.” See Abstracts.
A few existing methods for accomplishing non-circular-orbits for nuclear medicine cameras are now discussed with reference to FIGS. 7(A), 7(B) and 7(C).
With reference to FIG. 7(B), a first method is referred to as a “manually operated learn mode” method. In this method, a nuclear medicine technologist can pre-program an orbit by first manually moving the detector adjacent to a patient at a standard position (e.g., at 9:00 o'clock and 12:00 o'clock positions). The camera then calculates the orbit based on these manually determined positions. Then, the camera follows the calculated orbit during acquisition. One disadvantage of this type of method is the time required to move the detector to the standard position. In addition, because the pre-programming is performed manually, the likelihood of error is large.
With reference to FIG. 7(A), a second method for accomplishing a non-circular-orbit is referred to as an “auto-contour” method. As shown in FIG. 7(A), in this method, two rows of light beams are employed. The two rows of light beams b1 and b2 are used on each detector to maintain proximity to the patient P by maintaining the patient continuously between the rows of light beams as shown in FIG. 7(A). Among other things, this method has disadvantages related to the potential of creating sharp changes in the resolution during operation. In addition, the quality of the image deconstruction can be degraded by sharp jumps in image resolution from view to view. In addition, with dual detector systems that are reconfigured to, e.g., 90 degrees, there is what is known as the “dead zone” between detectors (see, for reference, zone Z in FIG. 4). When using an “auto-contour” method, to address the presence of a “dead zone,” it has been necessary to conduct a pre-scan around a patient P (see, e.g., FIG. 7(C)) to trace the non-circular-orbit, to add an offset, and then to execute the actual scan. Among other problems, a pre-scan adds a significant amount of time.
In addition to the foregoing, some illustrative methods and apparatuses are shown by way of example in the following references: (1) U.S. Pat. No. 6,255,656 entitled “Positioner for a Scintillation Camera Detector Head;” (2) U.S. Pat. No. 6,150,662 entitled “Gantry for Medical Imaging System;” (3) U.S. Pat. No. 6,114,701 entitled “Configurable Multiple Detector Nuclear Medicine Gantry;” (4) U.S. Pat. No. 6,055,450 entitled “Bifurcated Gamma Camera System;” (5) U.S. Pat. No. 5,929,446 entitled “Configurable Multiple Detector Nuclear Medicine Gantry;” (6) U.S. Pat. No. 5,866,906 entitled “Gamma Detector Locking Mechanism;” (7) U.S. Pat. No. 5,838,009 entitled “Variable Angle Multiple Detector Nuclear Medicine Gantry;” (8) U.S. Pat. No. 5,760,402 entitled “Dual-Head Medicine Imaging System With Cantilevered Detector Heads;” (9) U.S. Pat. No. 5,742,060 entitled “Medical System for Obtaining Multiple Images of a Body From Different Perspectives;” and (10) U.S. Pat. No. 5,523,571 entitled “Versatile Reconfigurable Gantry for Use In Scintillation Camera Systems.” All of the patents cited in this application are incorporated herein by reference in their entireties.
While a variety of methods and apparatuses are known, there remains a need for improved methods and apparatuses overcoming the above and/or other problems.